Structural basis of the 14-3-3 protein-dependent activation of yeast neutral trehalase Nth1.

BACKGROUND: Trehalases are highly conserved enzymes catalyzing the hydrolysis of trehalose in a wide range of organisms. The activity of yeast neutral trehalase Nth1 is regulated in a 14-3-3- and a calcium-dependent manner. The Bmh proteins (the yeast 14-3-3 isoforms) recognize phosphorylated Nth1 and enhance its enzymatic activity through an unknown mechanism. METHODS: To investigate the structural basis of interaction between Nth1 and Bmh1, we used hydrogen/deuterium exchange coupled to mass spectrometry, circular dichroism spectroscopy and homology modeling to identify structural changes occurring upon the complex formation. RESULTS: Our results show that the Bmh1 protein binding affects structural properties of several regions of phosphorylated Nth1: the N-terminal segment containing phosphorylation sites responsible for Nth1 binding to Bmh, the region containing the calcium binding domain, and segments surrounding the active site of the catalytic trehalase domain. The complex formation between Bmh1 and phosphorylated Nth1, however, is not accompanied by the change in the secondary structure composition but rather the change in the tertiary structure. CONCLUSIONS: The 14-3-3 protein-dependent activation of Nth1 is based on the structural change of both the calcium binding domain and the catalytic trehalase domain. These changes likely increase the accessibility of the active site, thus resulting in Nth1 activation. GENERAL SIGNIFICANCE: The results presented here provide a structural view of the 14-3-3 protein-dependent activation of yeast neutral trehalase Nth1, which might be relevant to understand the process of Nth1 activity regulation as well as the role of the 14-3-3 proteins in the regulation of other enzymes.

Role of individual phosphorylation sites for the 14-3-3-protein-dependent activation of yeast neutral trehalase Nth1.

Trehalases are important highly conserved enzymes found in a wide variety of organisms and are responsible for the hydrolysis of trehalose that serves as a carbon and energy source as well as a universal stress protectant. Emerging evidence indicates that the enzymatic activity of the neutral trehalase Nth1 in yeast is enhanced by 14-3-3 protein binding in a phosphorylation-dependent manner through an unknown mechanism. In the present study, we investigated in detail the interaction between Saccharomyces cerevisiae Nth1 and 14-3-3 protein isoforms Bmh1 and Bmh2. We determined four residues that are phosphorylated by PKA (protein kinase A) in vitro within the disordered N-terminal segment of Nth1. Sedimentation analysis and enzyme kinetics measurements show that both yeast 14-3-3 isoforms form a stable complex with phosphorylated Nth1 and significantly enhance its enzymatic activity. The 14-3-3-dependent activation of Nth1 is significantly more potent compared with Ca2+-dependent activation. Limited proteolysis confirmed that the 14-3-3 proteins interact with the N-terminal segment of Nth1 where all phosphorylation sites are located. Site-directed mutagenesis in conjunction with the enzyme activity measurements in vitro and the activation studies of mutant forms in vivo suggest that Ser60 and Ser83 are sites primarily responsible for PKA-dependent and 14-3-3-mediated activation of Nth1.